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Review Question - QID 106514

QID 106514 (Type "106514" in App Search)
A newborn is found to have cystic fibrosis during routine newborn screening. The parents, both biochemists, are curious about the biochemical basis of their newborn's condition. The pediatrician explains that the mutation causing cystic fibrosis affects the CFTR gene which codes for the CFTR channel. Which of the following correctly describes the pathogenesis of the most common CFTR mutation?

Insufficient CFTR channel production

9%

21/231

Defective post-translational glycosylation of the CFTR channel

64%

147/231

Excess CFTR channel production

0%

1/231

Defective post-translational hydroxylation of the CFTR channel

8%

18/231

Defective post-translational phosphorylation of the CFTR channel

19%

43/231

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The most common mutation in cystic fibrosis (CF) is deltaF508. This removes phenylalanine at the 508th position of the CFTR protein and causes defective post-translational folding and glycosylation.

Cystic fibrosis is the most common lethal genetic disease of the white population. It is caused by an autosomal recessive defect in the CFTR gene on chromosome 7. The mutation causes defective post-translational folding and glycosylation, resulting in degradation of the CFTR channel before reaching the cell surface. The CFTR gene codes for the CFTR channel which actively secretes Cl- in the lung and GI tract and actively reabsorbs Cl- from sweat. This defective Cl- channel causes secretion of abnormally thick mucus that plugs the lungs, pancreas, and liver and leads to the variety of symptoms seen in CF including recurrent pulmonary infection, pancreatic insufficiency, and meconium ileus in newborns.

Sawczak et al. describe novel therapeutic approaches in treating cystic fibrosis. They state the ultimate goal of treatment should be to correct dysfunctional CFTR proteins in CF patients. To that end, they state that S-nitrosothiols (SNOs), small, naturally occurring endogenous cell signaling compounds, may possibly increase CFTR maturation and function at the plasma membrane in human airway epithelial cells. However, clinical trials are still investigating the effectiveness and safety of these compounds.

Grosse et al. review the CDC guidelines for newborn screening for cystic fibrosis. The CDC currently recommends routine screening of all newborns for cystic fibrosis. This should be accompanied by rigorous infection control practices to minimize the risk to children with cystic fibrosis detected at an early age of acquiring infectious organisms associated with lung disease from older patients. Education of parents should play an important role in any screening programs.

Illustration A graphically demonstrates the post-translational deleterious effects of the CFTR mutation.

Incorrect Answers:
Answers 1 and 3: The quantity of the CFTR channel production is unchanged in the CFTR mutation. Rather, the quality in terms of post-translational modification is adversely affected.
Answer 4: The CFTR mutation results in defective post-translational glycosylation of the CFTR channel, not hydroxylation
Answer 5: The CFTR mutation results in defective post-translational glycosylation of the CFTR channel, not phosphorylation

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